1. Field of the Invention
This invention relates to an aqueous ink for ink jet recording. This invention particularly relates to an aqueous ink for ink jet recording, which does not scorch and stick to printing heads of ink jet printers and is capable of producing water-resistant images. This invention also relates to an ink jet recording method, in which the aqueous ink for ink jet recording is used.
2. Description of the Related Art
With ink jet recording systems, small droplets of an ink are directly jetted from a very small nozzle and caused to adhere to a recording medium, and images including characters are thereby produced on the recording medium. The ink jet recording systems have advantages in that the printing apparatus used produces less noise and have better operability, in that color images can be obtained easily, and in that plain paper can be used as a recording medium. Therefore, the ink jet recording systems have heretofore been used widely. Techniques for jetting the inks include, for example, piezo-electric techniques, which utilize piezo-electric devices for the printing heads, and thermal jet techniques which utilize heating resistor elements for the printing heads. Printers utilizing such techniques have heretofore been widely accepted in personal end use.
In order for the nozzles to be prevented from being clogged with inks, water-soluble dyes are conventionally used as the inks for ink jet printers. In cases where water-soluble dyes are used, the nozzles suffer from little clogging. However, the problems occur in that the water resistance of the obtained images cannot be kept high. Also, in cases where the thermal jet techniques are utilized, the problems occur in that the dyes undergo oxidation due to excessive amount of heat, and the inks are apt to scorch and stick to the printing heads.
With the thermal jet techniques, a heating resistor element is incorporated in the printing head, and the recording operation is carried out by boiling an ink with thermal energy generated by the heating resistor element to produce bubbles, and jetting small droplets of the ink by the action of the pressure of the resulting bubbles. Therefore, when the ink is heated and boiled on the heater, dyes contained in the ink often deteriorate and decompose. As a result, insoluble substances thus formed stick to the printing head and cause the printing head to be clogged. Accordingly, the composition of the ink is of great importance for preventing such clogging of the printing head.
Various attempts have heretofore been made to prevent an ink from scorching and sticking to a printing head. For example, a technique for utilizing an ink containing an organic sulfonate has been proposed in, for example, Japanese Patent Application Laid-open 4-227669. Also, a technique for utilizing an ink containing a dye having a specific structure has been proposed in, for example, U.S. Pat. No. 5,062,893. Further, a technique for utilizing an ink containing a salt of bile acid has been proposed in, for example, U.S. Pat. No. 5,108,501. However, none of the conventional techniques could achieve sufficient effects.
Also, various attempts have heretofore been made to improve the water resistance of printed images. For example, techniques for utilizing pigments as an ink have been proposed in, for example, Japanese Patent Application Laid-opens 4-28776, 4-189876, 4-359071, and 4-359072. Also, a technique for utilizing a non-aqueous liquid medium has been proposed in, for example, Japanese Patent Application Laid-opens 4-261478. Further, a technique for utilizing a dye having a high water resistance has been proposed in, for example, U.S. Pat. No. 4,963,189. However, if a pigment is used as an ink, the problems will occur in that the saturation of printed images cannot be kept high. Also, none of the other conventional techniques described above could substantially solve the problems with regard to the improvement in the water resistance.
Further, no ink has heretofore been proposed which can satisfy the two requirements described above in a well-balanced manner.